1. Field of the Invention
The present invention relates to an overrunning clutch.
2. Description of the Related Art
In rotating devices where one member (the "driving member") transmits torque to another member (the "driven member"), it is often advantageous to assure that torque is transmitted in one direction only and only from the driving member to the driven member. An automobile alternator is one such device.
As is well-known in the art, an automobile alternator is typically provided mechanical power from a V-belt attached to the automobile's engine. This belt drives a pulley, or sheave, on the alternator. This sheave proceeds to turn a shaft which drives a rotor in the alternator. The rotation of this rotor generates electricity.
A problem occurs, however, in the use of an alternator. This problem occurs when the engine is driving an alternator at a given speed and the automobile's transmission is in a given gear. If the transmission upshifts to a higher gear, the engine speed decreases abruptly. As a result, the V-belt driving the alternator abruptly decreases in speed as well. However, typical alternator rotors have considerable rotational inertia, which opposes the V-belt's abrupt decrease in speed. As a result, the alternator actually attempts to drive the V-belt. However, the interface between the V-belt and the sheave frequently cannot carry the resultant torque, which can be quite large. As a result, the V-belt may slip on the sheave, causing an audible and annoying squeal. An overrunning clutch, which would prevent the alternator from attempting to drive the V-belt in the manner just described, would prevent the squeal.
An overrunning clutch used in an alternator would typically take the form of an outer cylindrical "race", which would be connected to the sheave; and an inner cylindrical race, which would be connected to the alternator rotor. Engaging means arranged between the races would allow the V-belt to drive the alternator but would "overrun", not allowing torque transmission, when the alternator attempts to drive the V-belt.
The use of a simple roller-type overrunning clutch, well-known in the art, would help eliminate the belt squeal. However, roller-type clutches have springs which hold each roller member which engages the two races. At the high speeds experienced by an alternator (upwards of 18,000 revolutions per minute), the springs in a roller-type clutch will typically allow the engaging members to disengage from the two races. When the alternator speed reduces, the engaging members will re-engage, typically with a significant shock. Such a shock is a detriment to the reliability of the clutch.
U.S. Pat. No. 3,844,391 discloses an overrunning clutch which comprises sprags disposed between an inner and outer race. The sprags are held in engagement between the races by a spring. The sprags furthermore disengage by centrifugal force to prevent torque transmission from the driven race to the driving race. Although this configuration may be effective as an overrunning clutch, a more reliable and cost-effective design could result if the springs could be eliminated.
One additional concern in the design of an overrunning clutch for an alternator is due to a rather unique feature of an alternator. This feature is the driving of the alternator with a sheave. Because the sheave has a significant radius, such a driving mechanism causes substantial side loading on the alternator (typically in the range of 200 to 300 pounds). This loading causes an oscillation as the alternator rotates, which would cause the space between the races of an overrunning clutch to increase and decrease in size as the alternator rotates. Such an oscillation would tend to cause fretting wear of clutch members disposed between the races.
Therefore, an overrunning clutch which does not disengage at high speeds, which uses no springs, and which withstands side loading without oscillation will provide advantages over the prior art.